Current dilemma in photocatalytic CO2 reduction: real solar fuel production or false positive outcomings?

Abstract

Solar driven carbon dioxide (CO2) recycling into hydrocarbon fuels using semiconductor photocatalysts offers an ideal energy conversion pathway to solve both the energy crisis and environmental degradation problems. However, the ubiquitous presence of carbonaceous contaminants in photocatalytic CO2 reduction system and the inferior yields of hydrocarbon fuels raise serious concerns about the reliability of the reported experimental results. Here in this perspective, we focus on the accurate assessment of the CO2 reduction products, systemically discuss the possible sources of errors in the product quantification, elaborate the common mistakes spread in the analysis of reaction products obtained in 13CO2 labelling experiments, and further propose reliable protocols for reporting the results of these isotopic tracing experiments. Moreover, the challenges and cautions in the precise measurement of O2 evolution rate are also depicted, and the amplification of the concentration of O2 in photoreactors well above the limit of detection is still demonstrated to be the most effective solution to this troublesome issue. We hope the viewpoints raised in this paper will help to assessment the reliability of the reported data in future, and also benefit the beginners that intend to dive in the photocatalytic CO2 reduction area. Graphical abstract

Designing reliable and accurate isotope-tracer experiments for CO2 photoreduction

“…Even for the emerging synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) strategy, the existence of interfering factors induced by the long-time sampling is also uncertain 53 . So the gas chromatograph (GC) is essential to be added to the sampling system to separate molecular species before collecting mass spectra (MS) 54 , 55 .…”

Recent Advances on the Utilization of TiO2‐Based Catalysts in the Photocatalytic Reduction of CO2 to Methane

“…Among these, GC-MS is the widely used and reliable choice for tracking isotopes in CO 2 photoreduction. [122] GC-MS separates molecular species on the column based on affinity and measures mass-to-charge ratio (m/z) to distinguish isotope abundance [120,122] as shown in Figure 29. Notably, the major peaks for 13 CO 2 , 13 CH 4 , and 13 CO appear at m/z = 45, m/z = 17, and m/z = 29, respectively.…”

“…Various instruments, including nuclear magnetic resonance spectroscopy (NMR), [121] fourier transforms infrared spectroscopy (FT‐IR), [120] and gas chromatography‐mass spectrometry (GC‐MS) [67] can be employed for 13 C isotope‐tracing. Among these, GC‐MS is the widely used and reliable choice for tracking isotopes in CO 2 photoreduction [122] . GC‐MS separates molecular species on the column based on affinity and measures mass‐to‐charge ratio ( m/z ) to distinguish isotope abundance [120,122] as shown in Figure 29.…”

Doping of Vanadium into Bismuth Oxide Nanoparticles for Electrocatalytic CO2 Reduction

“…The reduction of CO 2 into usable fuels and derived chemicals through electrochemical methods is considered a very achievable strategy to reduce the growing CO 2 emissions and replace fossil energy. − Therefore, it is necessary and significant to develop electrochemical catalysts for CO 2 reduction reaction (CO 2 RR) with excellent activity, high selectivity, and superior stability. Bismuth (Bi) is a non-toxic and inexpensive material that can effectively suppress the hydrogen evolution reaction (HER) and has high selectivity for formate production. , However, the Bi-based catalysts usually require large overpotentials and present low current density, which hinders their practical applications. − …”